SF6 decomposition behaviour under partial discharge of typical insulation defects in gas-solid insulated valve-side bushing of converter transformer

In this paper we investigated SF6 decomposition behaviour of typical insulation defects in gas-solid insulated converter transformer valve-side bushing under partial discharge (PD). Additionally, we compared the results with that of gas insulated switchgear (GIS). The results indicated that SF6 decomposition behaviour varies with the insulation defects type. For metal protrusion defects, the proportion ranking of CO2 and SO2 can be related to whether the needle tip is wrapped with epoxy resin-impregnated paper (ERIP). The proportion of carbon-containing products is much higher under contamination defect than under other defects. Moreover, the proportion of carbon-containing components is higher under flashover condition than under PD condition and is accompanied by the appearance of H2S and CS2. However, the yield of SO2F2 is always low. Compared to negative DC voltages, positive DC voltages have a higher proportion of carbon-containing components, mainly in the form of more CO2 and less SOF2. Compared to the PD decomposition behaviour of typical insulation defects in GIS, when PD involves ERIP, the proportion of carbon-containing products, especially CO2, is significant higher, while the proportion of sulphur containing products, especially SO2F2, is lower.